Why would they do that, though? The thing the representatives care most about is getting re-elected. It's much easier (and productive to their interests) to point the finger at various other causes for economic decline than attempt to convince your constituents that bringing in immigrants is the solution. No one wants to be told that they are the problem, and "the other" needs to be brought in to fix it.

Many people are racist/xenophobic and don't want people of other races or cultures "taking over" their neighborhoods or towns. Even those who aren't actively racist are just resistant to change on that level, because it scares them.